The role of progesterone (P) and estrogen (E) in placental development is complex. In many instances P action first requires a background of E exposure to induce synthesis of the progesterone receptor (PR). The full consequence of these events is obscured by a lack of understanding of the direct regulatory effects of P per se on its own receptor and its reciprocal effects on the estrogen receptor (ER). We have developed a castrate pregnant rat model to study receptor mediated effects of E and P on the placenta. We propose that ER and PR dynamics are tissue specific and may vary at different stages of pregnancy. Our previous studies show that ER occur only in the decidua basalis (DB) whereas PR occur in DB and junctional zone (JZ); the labyrinth zone (LZ) is devoid of receptor. Yet, all three tissues are totally dependent on P-action for growth and differentiation. Thus, we propose specifically that the DB, JZ, and LZ are regulated either by the direct action of E and P or by paracrine factors elaborated in other hormone-responsive regions of the placenta. The present proposal is designed: l) to study how E and P interact to maintain ER and PR proteins and their cognate mRNAs; 2) to identify which placental regiOns express the ER and PR; and 3) to identify paracrine factors (e.g., EGF and placental lactogens, PLs) produced in culture under influence of E and P which regulate growth and differentiation of placental regions. Preliminary studies for this application establish the rationale and demonstrate that: l) exogenous P maintains ER and PR; 2) P induces at least two specific PLs; and 3) EGF receptors are abundant at all stages of pregnancy and are E and P insensitive. We will quantify induction of ER and PR in the DB, JZ, and LZ by immunocytochemistry and Western blot analysis. E and P interaction on ER and PR mRNAs will be evaluated by Northern and slot-blot analysis. Conditioned media from primary placental cell cultures derived from specific regions will be added to placental cells from other regions and assayed for ability of promote growth and proliferation. Production and identification of paracrine substances will be studied at various stages of pregnancy and under various hormone agonist and antagonist regimens. Our findings will establish the importance of the E and P receptor systems in maintaining pregnancy and will identify essential pregnancy specific proteins from the DB, JZ, and LZ. Findings from this project will increase our understanding of placental development and will lead to therapeutic prevention of Intra- Uterine Growth Retardation with its sequelae of fetal defects and even fetal loss which often result from placental dysfunction.